Heretofore, there has been known a battery provided with a battery case having a safety valve (an explosion-proof valve) of a non-restoring type and a protective film fixed to the battery case while externally covering the safety valve to seal the safety valve. This protective film is used to prevent foreign matters and liquid droplets such as water and oil from sticking to the safety valve, especially, its breakable portion having a thinner wall, thereby avoiding corrosion of the safety valve. For example, Patent Literatures 1 to 3 disclose a battery having such protective film.